1. Field of the Invention
The present invention relates to communication networks and, more particularly, to a method and apparatus for establishing forwarding state using path state advertisements.
2. Description of the Related Art
Data communication networks may include various computers, servers, nodes, routers, switches, bridges, hubs, proxies, and other network devices coupled to and configured to pass data to one another. These devices will be referred to herein as “network elements.” Data is communicated through the data communication network by passing protocol data units, such as Internet Protocol packets, Ethernet Frames, data cells, segments, or other logical associations of bits/bytes of data, between the network elements by utilizing one or more communication links between the devices. A particular protocol data unit may be handled by multiple network elements and cross multiple communication links as it travels between its source and its destination over the network. As used herein, the term “packet” will be used to refer to all types of protocol data units, not just IP packets.
Routing information on a network, such as the network illustrated in FIG. 1, may be exchanged using a variety of different protocols. One class of routing protocols that may be used to exchange routing information are commonly referred to as link state routing protocols.
Link state routing protocols use update messages to advertise routing information about links to which it is connected. Update messages will be referred to herein as Link State Advertisements (LSAs). Network elements on the network receive the LSAs and use the information from the LSAs to build a link state database representative of the topology of the network. Examples of common link state routing protocols include Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS), although other link state routing protocols may exist or be developed as well.
Another class of protocols, referred to herein as signaling protocols, are used to establish paths through the network so that traffic may be forwarded across the network along a particular path. For example, a network element may compute a path through the network by looking at its link state database, and then use a protocol such as Label Distribution Protocol (LDP) to cause labels to be distributed to form an MPLS label switched path across the network. In this example, once the labels have been distributed, the routers along the path will be able to forward data on the path from the source to the destination on the network so that all traffic intended to be carried by the path actually is able to follow the path through the network. Thus, the signaling protocol is used to cause the routers or other network elements on the path to install appropriate forwarding state for that traffic.
There are many different signaling protocols that have been developed to enable paths to be set up through the network. Examples of signaling protocols include Private Network to Network Interface (PNNI), Signaling System Seven (SS7), Reservation Protocol Traffic Engineering (RSVP-TE), and LDP which was mentioned above and is used with MultiProtocol Label Switching (MPLS), although there are undoubtedly other protocols as well that have been proposed or used to establish paths through a network.
Depending on the particular signaling protocol being used, the amount of overhead required to signal a particular path may vary significantly, although generally most signaling protocols require each path to be established individually. Hence, signaling paths on the network may consume significant resources particularly where there are large numbers of paths to be established or altered.